Heat-seeking (infrared) detection systems employed by missiles, other weapons, or devices can detect the infrared radiation emitted by hot gas exhaust structures on military targets, such as ships, aircraft, or ground installations. These devices employ this radiation for weapon guidance, or for reconnaissance and classification purposes. The infrared detection vulnerability of military targets can be reduced by decreasing the temperatures of the hot gas exhaust structures such as ships' stacks.
The prior art shows at least two unsuccessful schemes for the reduction of steam-ship stack temperatures. The first scheme involves the use of sea water sprayed into the stack gases and cavity. This reduced the infrared radiation by one-half, and is not sufficient to defeat known infrared detection systems. The second scheme uses ambient air which, after traversing cooling passages, is aspirated into the exhaust gas path within the smokepipe. Due to the design of the smokepipe and since power conditions are frequently changed, exhaust velocities would change and result in an uncontrolled situation. Additionally at relatively low exhaust gas velocities, the flow of the hot exhaust gases through the cooling passages might result rather than their flowing out of the top of the stack, thus defeating the intent of the scheme. The second scheme also uses a single-walled shield to prevent low-angle viewing into the smokepipe, but such a shield is, itself, susceptible to heating by wind-blown exhaust gases, a condition which would defeat its purpose.